Convection ovens and dryers that process continuous streams of product are in wide use in both industrial and baking applications. In many ovens the product moves horizontally on one or more levels, either carried on parallel moving conveyors or, in the case of textiles or webs, suspended under tension between external drives. A circulating hot air flow is brought in contact with the product for heating or drying.
Certain means of providing airflow are known in the industry. U.S. Pat. No. 6,712,064 discloses an oven with multiple nozzles arranged both above and below the product conveyor, with the vertically directed airflow impinging the product at nearly a right angle. U.S. Pat. No. 6,539,934 and U.S. Pat. No. 6,684,875 describe impingement flow ovens with multiple parallel conveyors. These patents disclose that pressurized air from a fan discharge is distributed uniformly over the product by means of nozzles containing one or two perforated plates. Since the air flow contacts the product a very small distance from the nozzle discharge, it is not necessary that the nozzle provide airflow in a straight direction from the nozzle face.
For delicate products that can be damaged by perpendicular impingement flow, there is an advantage to having the air flow parallel to the product. U.S. Pat. No. 4,515,561 discloses an oven with airflow parallel to and in the same direction as product travel, with sets of nozzles arranged above and below the product and connected to the fan discharge header at the side of the oven. In this oven configuration the air contacts the product for a large distance, essentially the length of the oven, after leaving the nozzle.